An Investigation of the Use of 16 and 18 AWG
Conductors for Power Branch Circuits in
Industrial Machinery Applications
for
NFPA79 Small Wire Working Group
by
Underwriters Laboratories Inc.
Northbrook, IL 60062
August 10, 2001
Project Number 01NK27019
File Number E4273
Sponsored by
Bussmann Div., Cooper Ind.
Ellisville, MO 63021
Copyright 2001 Underwriters Laboratories Inc.
Underwriters Laboratories Inc. authorizes the above named company and committee to
reproduce this report provided it is reproduced in its entirety.
i
NOTICE
In no event shall UL be responsible to anyone for whatever use or non-use is made of the
information contained in this Report and in no event shall UL, its employees, or its agents
incur any obligations or liability for damages including, but not limited to consequential
damage arising out of or in connection with the use or inability to use the information
contained in this Report.
Information conveyed by this Report applies only to the specimens actually involved in these
tests. The wire samples tested were provided by the applicant and UL neither selected the
samples nor determined that they were representative of the finished assembly.
The issuance of this Report does not constitute an endorsement of any proposed amendment
to or existing text in any nationally recognized installation code or standard. This Report in
no way implies any additional Listing, Classification, or Recognition by UL and does not
authorize the use of UL Listing, Classification, or Recognition Marks or any other reference
to UL in connection with the product or system.
ii
TABLE OF CONTENTS
NOTICE..................................................................................................................................................................................................................... II
TABLE OF CONTENTS .....................................................................................................................................................................................III
BACKGROUND AND SUMMARY ..................................................................................................................................................................1
SUMMARY OF RESULTS.........................................................................................................................................................................................2
INTRODUCTION...................................................................................................................................................................................................3
INDUSTRY NEED TO UTILIZE SMALL CONDUCTORS .........................................................................................................................................3
EXISTING REQUIREMENTS....................................................................................................................................................................................3
INDUSTRY NEEDS...................................................................................................................................................................................................3
ENGINEERING A NALYSIS.......................................................................................................................................................................................3
Normal Operating Current.............................................................................................................................................................................4
Inrush Characteristics......................................................................................................................................................................................4
Thermal Withstand Ratings for Insulated Conductors - Various Methods.............................................................................................4
Determination of the Thermal Withstand Ratings for 16 and 18 AWG conductors.............................................................................8
Magnetic Withstand for Insulated Conductors............................................................................................................................................9
Selection of Overcurrent Protective Devices...............................................................................................................................................9
Testing.............................................................................................................................................................................................................. 11
PLAN OF INVESTIGATION ........................................................................................................................................................................... 12
GENERAL CONSIDERATIONS...............................................................................................................................................................................12
VERIFICATION OF SHORT -CIRCUIT PROTECTION OF CONDUCT OR................................................................................................................12
VERIFICATION OF OVERLOAD PROTECTION OF CONDUCTOR........................................................................................................................15
Motor Loads.................................................................................................................................................................................................... 15
Non-Motor Loads........................................................................................................................................................................................... 16
Inspection of Wire.......................................................................................................................................................................................... 16
Insulation Dielectric Withstand Tests ........................................................................................................................................................ 16
TEST DATA, OBSERVATIONS, AND RESULTS .................................................................................................................................... 18
Test Data Sheet............................................................................................................................................................................................... 18
Test Observations.......................................................................................................................................................................................... 18
Assessment of Results.................................................................................................................................................................................... 18
IOGRAPHY............................................................................................................................................................................................................. 84
ANNEX A ................................................................................................................................................................................................................ 86
ANNEX B ................................................................................................................................................................................................................ 92
ANNEX C................................................................................................................................................................................................................ 93
INDEX ..................................................................................................................................................................................................................... 97
iii
E4273
Issued: 8-10-01
BACKGROUND AND SUMMARY
In order to remain competitive in the global marketplace, United States industrial machinery
manufacturers on the committee for NFPA79 (Electrical Standard for Industrial Machinery) expressed the
need to be able to utilize power circuit conductors which are smaller than 14 AWG, the existing minimum
allowed for branch circuits in the United States. This report details the investigation and testing that was
conducted to investigate the use of 16 and 18 AWG conductors for power branch circuits. Various fuse type
overcurrent protective devices, including commercial fuses and special test fuses (unbrella) were used for the
investigation. The testing considered the performance of 16 and 18 AWG conductors under these
conditions:
•
•
•
Short Circuit
Overload
Use on various electrical systems
Following the testing, the conductors were subjected to a dielectric withstand test on the insulation. The
results of the study are summarized in the table below.
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Issued: 8-10-01
Summary of Results
Test
#
Test 1A
Test 1B
Test 1C
Test 1D
Test 1E
Test 1F
Test 2A
Test 2B
Test 2C
Test 2D
Test 2E
Test 2F
Test 3A
Test 3B
Test 3C
Test 4A
Test 4B
Test 4C
Test 5B
Test 5C
Test 6B
Test 6C
Test 6E
Test 6F
Test 7A
Test 7B
Test 7C
Test 8A
Test 8B
Test 8C
Test 9B
Test 9C
Volts Phase Current
(Amps)
LV
LV
LV
LV
LV
LV
LV
LV
LV
LV
LV
LV
480
480
480
480
480
480
480
480
480
480
480
480
600
600
600
480
480
480
480
480
1
1
1
1
1
1
1
1
1
1
1
1
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
1
1
15
48
15
33
11
48
15
30
15
21
8
34
5000
10,000
50,000
5000
10,000
50,000
10,000
50,000
10,000
50,000
10,000
50,000
5000
10,000
50,000
5000
10,000
50,000
10,000
50,000
Overcurrent
Protective
Device
Commercial Fuse
Commercial Fuse
Commercial Fuse
Commercial Fuse
Commercial Fuse
Commercial Fuse
Commercial Fuse
Commercial Fuse
Commercial Fuse
Commercial Fuse
Commercial Fuse
Commercial Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
Umbrella Fuse
2
Wire Conductor Maximum I t Visual Inspection
Size Thermal Let Through Observation
Withstand (Amps 2 sec)
(Amps 2 sec)
16
18,657
N/A
No Visible Damage
16
18,657
N/A
No Visible Damage
16
18,657
N/A
No Visible Damage
16
18,657
N/A
No Visible Damage
16
18,657
N/A
No Visible Damage
16
18,657
N/A
No Visible Damage
18
7,355
N/A
No Visible Damage
18
7,355
N/A
No Visible Damage
18
7,355
N/A
No Visible Damage
18
7,355
N/A
No Visible Damage
18
7,355
N/A
No Visible Damage
18
7,355
N/A
No Visible Damage
16
18,657
1,690
No Visible Damage
16
18,657
1,980
No Visible Damage
16
18,657
1,420
No Visible Damage
18
7,355
1,420
No Visible Damage
18
7,355
1,440
No Visible Damage
18
7,355
1,450
No Visible Damage
18
7,355
7,010
No Visible Damage
18
7,355
5,140
No Visible Damage
16
18,657
820
No Visible Damage
16
18,657
1,230
No Visible Damage
18
7,355
1,000
No Visible Damage
18
7,355
1,280
No Visible Damage
18
7,355
8,290
No Visible Damage
18
7,355
10,400
No Visible Damage
18
7,355
6,330
No Visible Damage
18
7,355
7,070
No Visible Damage
18
7,355
8,120
No Visible Damage
18
7,355
7,900
No Visible Damage
18
7,355
6,690
No Visible Damage
18
7,355
6,130
No Visible Damage
2
Dielectric
Testing
Results
(Pass/Fail)
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
E4273
Issued: 8-10-01
INTRODUCTION
Industry Need to Utilize Small Conductors
In order to remain competitive within the global marketplace, United States industrial machinery
manufacturers on the committee for NFPA79 (Electrical Standard for Industrial Machinery) expressed
the need to be able to utilize power circuit conductors that are smaller than 14 AWG, the existing
minimum allowed for branch circuits in the United States. Several proposals were written and
submitted for NFPA79 adoption. However, a study was requested to confirm the theoretical
engineering analysis utilized for the substantiation of the proposals. This Report details the results of
that study.
Existing Requirements
The general requirements for the 1999 edition of National Electrical Code (NEC ) and the 1997
edition of NFPA79 Electrical Standard for Industrial Machinery currently do not allow conductors
smaller than 14 AWG to be utilized for power branch circuits. In the NEC the requirements are
found in sections 210-19 and 310-5. In NFPA79 the requirements are found in subclause 15.3.
Industry Needs
The industrial machinery industry has recognized the need to utilize 16 and 18 AWG conductors for
both motor and non-motor loads. Wire sizes of 0.75 mm2 and 1 mm2 are commonly applied where the
load currents are very small in applications based upon IEC 60204-1 (Safety of Machinery – Electrical
Equipment of Machines). Wire sizes of 0.75 mm2 and 1 mm2 have an ampacity similar to 18 AWG
and 16 AWG wire respectively.
Engineering Analysis
An engineering-based analysis was completed on the properties of 16 and 18 AWG conductors. This
analysis, developed by the NFPA Small Wire Working Group, and designed to cover typical “worst
case” overcurrent conditions as might be found in various types of electrical distributions, is included
here.
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ENGINEERING ANALYSIS
(Developed by the NFPA Small Wire Working Group)
Background
The analysis could best be summarized by the requirements in subclause 8.1.2 of NFPA79 shown here:
(d) Load and circuit component characteristics.
1)
Normal operating current.
2)
Inrush characteristics.
3)
Thermal withstand capability (I2 t).
4)
Magnetic withstand capability (Ip).
Normal Operating Current
First normal operating current was considered per NFPA79 8.1.2 (d) (1). The UL standard for
Industrial Control Equipment, UL508, provides ampacities for 16 and 18 AWG conductors. The
information is summarized in Table 1 below as follows:
Table 11
Wire Size
16 AWG
18 AWG
Copper Conductors
Insulation Rating
60°C
60°C
Ampacity
10 amps
7 amps
Inrush Characteristics
Further engineering analysis explored the nature of the loads that the smaller conductors would supply.
Research of the types of devices to be used for these loads was explored. As stated earlier, the desire
from the NFPA79 committee was to utilize this small wire on motor and non-motor loads. For motor
loads, the analysis included the use of motor starters for overload protection along with a branch
circuit, overcurrent protective device for short-circuit protection. For non-motor loads, the analysis
included the use of only a single branch circuit overcurrent device.
Thermal Withstand Ratings for Insulated Conductors - Various Methods
The next step in the analysis was to explore the withstand capabilities of the small wire, as required in
NFPA79 subclause 8.1.2 (d) (3). Withstand capabilities of insulated cable pertains to the level of
short-circuit current an insulated conductor can handle for a certain amount of time. Insulated
conductors are components of an electrical system and are required to be protected against “excessive
damage” per the NEC  in section 110-10 and NFPA79 subclause 8.1.2.
Research of available literature was conducted on the effects of short-circuit currents on insulated
conductors. The findings of four different methods were analyzed to determine the most appropriate
method to use for this analysis. The four different methods included:
•
•
•
•
1
Insulated Cable Engineers Association Standard P-32-382
Research conducted by William H. Middendorf
“Grounding Electrical Systems for Safety,” Eustice Soares
Onderdonk melting point
Information obtained from UL508, August 22, 2000, Section 43 Table 43.2
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Issued: 8-10-01
The Insulated Cable Engineers Association (ICEA) standard P-32-382 provides a standard physics
formula for determining the short-circuit withstand of insulated copper conductors.
The formula is as follows:
2
 T2 + 234 
I 
 A  t = 0.0297 log  T + 234 
 1

I = Short-circuit Current – Amperes
A = Conductor Area – Circular Mils
t = Time of Short-circuit - Seconds
T1 = Maximum Operating Temperature
T2 = Maximum Short-circuit Temperature
Physics Equation 1 – ICEA Conductor Withstand Formula
This physics formula for determining the heat rise for a specific cross sectional area of copper was
used to create a worst case condition for the wire. The formula utilized by ICEA was based upon an
adiabatic process where all the heat is contained within the wire. ICEA, using the standard physics
formula, determined maximum short-circuit temperatures for conductors with various types of
insulation as shown:
• Thermoplastic (150 °C)
• rubber, paper, varnished cloth (200 °C)
• Crosslinked Polyethylene & Ethylene Propylene Rubber (250 °C)
The temperatures specified above designate the start of insulation damage. Using the most
conservative approach, thermoplastic insulation (150°C) has the lowest short-circuit temperature of the
types tested. Inserting 150 °C for T2 into physics equation 1, would generate I2 t values as shown in
Table 2.
Table 2
ICEA I2 t Withstand Limits for Copper Conductor,
Thermoplastic Insulation (75°C)
(No Insulation Damage)
Wire Size
Short-circuit Withstand I2 t
14 AWG
47,000 A2 s
12 AWG
120,000 A2 s
10 AWG
303,000 A2 s
Studies conducted by William H. Middendorf of the University of Cincinnati explored the effects of
short-circuit currents on insulated conductors. The studies were conducted to evaluate the damage
levels referenced in the ICEA standard P-32-382. The purpose was to evaluate the accuracy of the
ICEA damage levels. As a result, Middendorf derived withstand limits different from the levels
achieved by ICEA. The withstand levels derived from this research were based upon the amount of I2 t
that would cause the dielectric strength of the insulation to be half the value of untested wire. As
expected, the I2 t levels required to reduce the dielectric strength of the wire were greater than those for
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which there was no insulation damage (ICEA). The I2 t values resulting from this research are shown
in Table 3.
Table 3
Middendorf I t Withstand Limits for Copper Conductor,
Thermoplastic (THW-75°C) Insulation
(Insulation Damage to ½ of Original Dielectric)
Wire Size
Short-circuit Withstand I2 t
14 AWG
150,000 A2 s
12 AWG
450,000 A2 s
10 AWG
1,100,000 A2 s
2
Eustice Soares wrote, “Grounding Electrical Systems for Safety.” Soares provides another reference
level for conductor withstand. Soares states that the validity rating for conductors corresponds to the
amount of energy required to cause the copper to become loose under a lug after the conductor has had
a chance to cool back down. This “validity” rating is based on raising the copper temperature from
75°C to 250°C. Using physics equation 1, the I2 t withstand levels of conductors that will become loose
under a lug is shown in Table 4 below.
Table 4
Soares I t Withstand Limits for Copper Conductor,
(Copper No Longer Tight Under Lug)
Wire Size
Short-circuit Withstand I2 t
14 AWG
94,000 A2 s
12 AWG
238,000 A2 s
10 AWG
599,000 A2 s
2
The final method, by Onderdonk, provides the withstand level that represents the amount of I2 t
required to cause copper conductors to melt. Onderdonk determined the short-circuit temperature to be
1083°C. Inserting this temperature into physics equation 1, the I2 t withstand levels for melting of
copper is as shown in Table 5.
Table 5
Onderdonk I t Withstand Limits for Copper Conductor,
(Melted Copper)
Wire Size
Short-circuit Withstand I2 t
14 AWG
320,000 A2 s
12 AWG
804,000 A2 s
10 AWG
2,300,000 A2 s
2
In addition to the analysis just discussed, both United States and International standards were
researched to explore procedures already utilized in the United States and other parts of the world for
short-circuit protection of conductors.
The Institute of Electrical and Electronics Engineers (IEEE) recommends the short circuit protection of
insulated conductors, using the ICEA physics formula in equation 1, in standards:
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•
•
•
•
Issued: 8-10-01
ANSI/IEEE 141-1993 (Red Book) sections 5.6.2 and 12.4.6
ANSI/IEEE 241-1990 (Gray Book) sections 8.5.6 and 9.8.7.1
ANSI/IEEE 242-1986 (Buff Book) section 8.4.2
ANSI/IEEE 1015-1997 (Blue Book) section 4.11.1.2
Various machinery standards also recommend the short circuit protection of insulated conductors using
a formula similar to the ICEA physics formula in Equation 1, with conversion factors being the
difference. These standards also state the insulation damage level for thermoplastic insulation is at
160°C as compared to the 150°C level used by ICEA. The machinery standards that suggest this
approach include:
• IEC60204-1 1997 section 13.1 and Annex C section C.4
• SAE HS-1738 2000 section 13.1 and Annex C section C.4
IEC60204-1 is the accepted machinery standard in Europe. SAE HS-1738 is the accepted machinery
standard for the United States automotive industry.
The International Electrotechnical Commission (IEC) standard 60364-4-43 1997 requires short-circuit
protection of conductors, using a formula equal to physics equation 1 (with conversion factors being
the difference), see equation 2.
θ f + β 

I 2t = K 2 S 2 ln 
θ
+
β
 i

K = conductor material constant
= 226 for copper
S = cross sectional area of conductor, mm2
θf= final temperature of conductor, °C
θI= initial temperature of conductor, °C
β = reciprocal of temperature coefficient of
resistance for conductor material at 0°C, °C
= 234.5 for copper
Equation 2 – IEC Conductor Withstand Formula
The Canadian Electrical Code (CEC), C22.1-98 Safety Standard for Electrical Installations,
recommends the ICEA method for determination of conductor protection in Appendix B.
After researching the above methods along with the ANSI, CEC, and International approaches, the
safest approach was to analyze the withstand limits using the most conservative method. The physics
formula, as promoted by ICEA, was the most conservative, see Table 6, as well as most used, and was
therefore used to analyze 16 and 18 AWG insulated conductors.
Table 6
ICEA I2t Withstand Limits Copper Conductor, Thermoplastic Insulation (75°C)
Wire Size
ICEA
Middendorf
Soares
Onderdonk
14
47,000
150,000
94,000
320,000
12
120,000
450,000
238,000
804,000
10
303,000
1,100,000
599,000
2,300,000
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Determination of the Thermal Withstand Ratings for 16 and 18 AWG conductors
Short-circuit Withstand Ratings
Using physics equation 1 and cross sectional area from NEC  Table 8, thermal I2 t withstand ratings for
16 and 18 AWG insulated conductors were calculated, see Table 7.
Table 7
ICEA I t Withstand Limits Copper Conductor, Thermoplastic Insulation (75°C)
Wire Size
Short-circuit Withstand I2 t
18 AWG
7,355 A2 s
16 AWG
18,657 A2 s
2
Physics equation 1 could also be used to calculate the maximum short-circuit current an insulated
conductor can withstand for a specified amount of time. This type of analysis was conducted at the
NFPA79 committee meetings. See Annex A for details on this analysis.
Medium Range Overcurrent Capabilities
While the withstand temperatures of insulated cables under short-circuit conditions has been
thoroughly researched, medium range overcurrent capability research is not as plentiful. This is
partially due to the fact that this condition can not really be considered adiabatic, and the dissipation of
heat from the conductor into the system varies greatly from installation to installation. Since the
formula developed by ICEA, physics Equation 1, assumes an adiabatic condition, this would constitute
a “worse case” condition for the conductor, with no heat loss to the system, and was used in this
analysis for a conservative approach. The amounts of current that 16 and 18 AWG conductors could
handle under overload conditions are summarized in Table 8 and Table 9. This type of analysis was
conducted at the NFPA79 committee meetings. See Annex A for details on this analysis
Table 8
16 AWG Withstand Overload Conditions (75°C)*
Duration of Overcurrent (seconds)
Withstand Current
1
137
5
61
10
43
* Data based upon formula in ICEA Publication P-32-382, See Equation 1
Table 9
18 AWG Withstand Overload Conditions (75°C)*
Duration of Overcurrent (seconds)
Withstand Current
1
86
5
38
10
27
* Data based upon formula in ICEA Publication P-32-382, See Equation 1
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Issued: 8-10-01
Magnetic Withstand for Insulated Conductors
Another step in the analysis is to analyze the magnetic withstand capabilities of the small wire, as
required in NFPA79 subclause 8.1.2 (d) (4). The proper analysis of the magnetic withstand limits is
best conducted via testing. This analysis is currently conducted in product testing via assurance that
the conductor cannot pull out of any termination as a result of testing. For this investigation, the
magnetic withstand capabilities will be addressed by testing.
Selection of Overcurrent Protective Devices
The major properties, current carrying capacity and short-circuit withstand required for proper
application of insulated conductors have been determined. Now proper overcurrent protection needs to
be determined.
Using the properties that have been documented, overcurrent protective devices that will carry the
rated current and protect the insulated conductor against overcurrents must be chosen.
Short-circuit Protection
The overcurrent protective devices will need to limit the energy let-through, of short-circuit currents, to
a level below the short-circuit thermal withstand of the 16 and 18 AWG conductors as specified in
Table 7. Knowing this, various overcurrent protective devices can be explored.
UL/CSA/ANCE 248 Current Limiting Fuses
Originally current limiting devices were chosen by the NFPA79 adhoc committee in order to easily
cover the variety of fault current conditions that exist upon which the machine may be applied. Listed
current limiting fuses are classified by umbrella limits published in the UL/CSA/ANCE 248 series of
standards. The umbrella limits provide maximum permissible let through values for instantaneous peak
current and I2 t for a specific class of fuse and ampere rating. In order for a current limiting fuse to
achieve listing, the let through values of the fuse must be less than the umbrella limits required for that
class and ampere rating of fuse. The umbrella limits governing current limiting fuses provide a sound
way of performing engineering analysis. In addition to the UL/CSA/ANCE 248 series of standards,
the UL White book, General Information for Electrical Equipment Directory, provides the umbrella
limits for the various classes of current limiting fuses. Upon examination of the White book, the I2 t
and peak let through currents of various current limiting branch circuit fuses were evaluated. Initially,
Class CC fuses, 20 amps and below, were found to protect both the 16 and 18 AWG wire according to
limits set forth. See Table 10. Class CC fuses 20 amps and below were used in the analysis that was
conducted at the NFPA79committee meetings. See Annex A for details on this analysis
Table 10
UL Class CC Umbrella Limits
Current Rating
15
20
Between Threshold
and 50KA
Ip (A)
I2 t (A 2 s)
3,000
2,000
3,000
2,000
At 100 KA
Ip (A)
3,000
4,000
I2 t (A 2 s)
2,000
3,000
At 200KA
Ip (A)
4,000
5,000
I2 t (A 2 s)
3,000
3,000
Further research of current limiting fuses using the umbrella limits, expanded the list of potential
devices to include Class J, T, and CC fuses up to 30 amps. A review of the umbrella limits for the
Class J, T, and CC 30 amp fuses showed that the maximum permissible I2 t limits for these fuses are
less than the wire limits shown in Table 7. See Table 11 below:
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Issued: 8-10-01
Table 11
UL Class of Fuse
Current Rating
Class CC
Class J
Class T (600V)
30
30
30
Between Threshold
and 50KA
Ip (A)
I2 t (A 2 s)
6,000
7,000
6,000
7,000
6,000
7,000
At 100 KA
Ip (A)
7,500
7,500
7,500
At 200KA
I2 t (A 2 s)
7,000
7,000
7,000
Ip (A)
12,000
12,000
12,000
I2 t (A 2 s)
7,000
7,000
7,000
Overload Protection
The overcurrent protective device needs to interrupt low level overloads prior to thermal damage of the
conductor insulation. Two major types of branch circuit loads were included in this analysis, motor
loads and non-motor loads. For motor loads, an overload relay as part of a motor starter, is used for
this purpose. This motor starter is used in conjunction with a branch-circuit short-circuit protective
device as it would be applied in the field.
The standard used to investigate overload relays and motor starters is UL508. Overload relays can be
classified according to their tripping time at 600 percent of their current rating. The classification is
outlined in Table 12.
Table 12
Class Designation for Overload Relays per UL508*
Class Designation
Tripping Time @ 600% (sec)
Class 10
10
Class 20
20
Class 30
30
* Data based upon UL Standard 508 Table 146.1
For non-motor loads a single branch circuit overcurrent protective is used. This device must be
capable of interrupting both short-circuit and overload currents. Current limiting fuses tested to
UL/CSA/ANCE 248 undergo low level testing as outlined in Table 13.
Table 13
UL248 Test Points*
Test Level
(% Rated Current)
135
200
* For fuses 30 amps and less
Opening Time
(min)
60
4
The data shown in Tables 12-13 provide reference levels for opening times of overcurrent protective
devices under overload conditions. These levels are used to evaluate the performance of the various
overcurrent protective devices compared to the withstand of 16 and 18 AWG conductors. This type of
analysis was conducted at the NFPA79 committee meetings, See Annex A for details on this analysis
10
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Testing
The next step in the process evaluates the suitability of 16 and 18 AWG insulated conductors for
power branch circuits with actual testing. Testing was designed to cover a broad range of overcurrents,
overload and short-circuit, in order to analyze the suitability of 16 and 18 AWG conductors for power
branch-circuit application. The plan for investigation, test data and results, and analysis of the results
are contained in the remainder of this report.
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Issued: 8-10-01
PLAN OF INVESTIGATION
General Considerations
In order to provide data to support the Engineering Analysis provided by the NFPA Small Wire
Working Group, a test program was developed by the Working Group with three major principles:
1. Create tests using conservative approaches simulating worst case conditions
- “Bus bar” testing from UL489
- Umbrella fuses for short circuit testing
- 1’, 4’, and 100’ lengths of wire
2. Create tests to cover various types of electrical systems and grounding schemes
- Full voltage, high current testing on each pole
3. Check validity of wire insulation via dielectric testing
- Per UL83, Thermoplastic Insulated Wire and Cable , section 27
Test setups hinged around these three major principles and were used in the plan for investigation. UL
standards 508, 489, and 248 were used as the base documents for the testing. The actual test
configurations deviated from these test configurations only to create worst case conditions, and account
for real application scenarios for industrial machinery.
The test program explored the suitability of 16 and 18 AWG insulated conductors for use on power
branch circuits. The test program was divided into two major categories: Verification of Overload
Protection of Conductor and Verification of Short-circuit Protection of Conductor. Following the testing
the conductor was tested for insulation damage via dielectric testing outlined in UL83, section 27.
Verification of Short-circuit Protection of Conductor
Testing was performed to investigate the short-circuit protection of 16 and 18 AWG cable. Development
of the test setups was based upon creating tests that would cover the majority of the applications for
which the wire would be installed. A conservative approach using “worst case” test situations was used
for this development.
The first step was to determine the test configuration for the short-circuit testing. In order to cover the
variety of installations that could exist, it was determined that, initially, 1 foot and 100 foot lengths of
conductor would be used in the testing, see Figures 1 and 2.
Figure 1 – 1 foot Test Setup
Figure 2 – 100 foot Test Setup
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Issued: 8-10-01
The 1 foot length would investigate the thermal and magnetic withstands of short runs of conductor
inside a cabinet. The 100 foot test setup investigated the thermal and magnetic withstands of long runs
of conductor.
A conditional test with 4' of conductor was also used on the high fault level testing for the devices that
passed the 1 foot test. The 4' length would provide an additional check on the magnetic withstand of the
conductor.
Figure 3 – 4 foot Test Setup
Bolted fault conditions were used to coincide with existing testing configurations employed by UL in
standards UL/CSA/ANCE 248, UL489, and UL508 and to give to a worst case short-circuit condition.
The fault was created directly at the end of the run of the conductor, see Figures 1, 2, and 3. Connection
to the test lab terminals followed the "bus bar" high fault circuit test configurations in UL 489. The "bus
bar" test conditions in UL489 require 4' of #1 conductor feeding the line lugs of the OCP device and 10"
of rated wire in the load side. One foot of rated wire was used instead of 10" for simplicity. For all the
short-circuit testing using fuses, umbrella fuses were used. This follows the existing requirements in
standards UL/CSA/ANCE248, UL489, and UL508 and creates a worst case situation, since any listed
commercially available fuse will perform better than the umbrella fuses. See Annex B for data on
umbrella fuses used in the test program. Note in Annex B that there is not an upper limit on the
instantaneous peak current and I2 t let through when selecting umbrella fuses. In this testing, for
example, the I2 t was more than double the umbrella limit.
A wide variety of short-circuit current levels were used to cover the variance in installations and fault
levels in the industry. The following short-circuit current levels were used in the testing:
• 50,000 amps
• 10,000 amps
• 5,000 amps
The 50kA level was chosen based upon UL/CSA/ANCE 248 fuse testing and the work conducted by the
NFPA79 Committee. See annex A. Since the I2 t umbrella limit of Class CC, J, and T fuses are the same
at 50, 100, and 200kA, the 50kA level was determined to represent the high short-circuit current testing
level. The 50kA test was conducted on all of the branch-circuit short-circuit devices tested with varying
power factors. The 10kA level is a common test level used in various UL standards for low level short13
E4273
Issued: 8-10-01
circuit current testing. All of the branch-circuit, short-circuit devices were tested at this level. The 5kA
test level was selected to cover the lower end of the short-circuit current spectrum. This testing was
limited to the stand alone branch-circuit, short circuit devices and the 1' test configuration.
The 1, 4, and 100 foot tests were performed at 480V, 3 phase with varying power factors. Conditional
tests at a full 600V were performed on the branch-circuit, short-circuit devices that passed all the 480V
testing, see Figure 1 for setup. This test sequence was conducted for the 5, 10, and 50kA tests.
Additional test configurations were utilized to investigate various commonly used grounding schemes.
The test configurations were used to verify the suitability of the conductors where the maximum
possible I2 t, instantaneous peak current, and voltage would be imposed on the conductor pertaining to
the various systems. The four main types of systems investigated were:
Solidly grounded WYE
Corner grounded Delta
Resistance grounded WYE
Ungrounded systems
The three phase bolted fault test configuration described previously covered the solidly grounded wye
system. Additional test configurations were used to investigate the remainder of the systems. A fault
was created across one pole of the branch-circuit, short-circuit devices using line to line voltage. This
would simulate a situation that could exist in these grounding schemes where single or multiple line to
ground faults could impose line to line voltage across one pole of the device. The test setup is shown in
Figure 4.
14
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Issued: 8-10-01
Figure 4 – Test Setup for Corner Grounded Delta,
Resistance Grounded Wye, and
Ungrounded Systems
The 50kA and 10kA fault levels were used for this test configuration. Only the stand alone branchcircuit, short-circuit devices were investigated.
Verification of Overload Protection of Conductor
At the end of the short circuit testing, the devices that passed were subjected to overload testing. In
order to investigate overload protection of 16 and 18 AWG conductors, testing was performed to explore
overcurrent protection for two different types of loads: motor loads and non-motor loads.
Motor Loads
In order to investigate motor branch circuits, motor starters were used in conjunction with branch-circuit
short-circuit protective devices that they were listed with. Both class 10 and class 20 overload relays
were used in the test program. Class 20 overload relays are more popular, but as shown below, the use
of class 10 overloads could lead to a larger permissible load current. See Annex A for details on this
analysis. As a result of the work conducted by the NFPA79 adhoc committee, limitations were placed on
the load current for 16 and 18 AWG conductors depending on the class overload relay used. These
current levels are shown in Table 15.
Overload Relay Class
10
20
Table 15
Maximum Full Load Currents for Motor Loads
16 AWG
18 AWG
Maximum Full Load Ampacity
Maximum Full Load Ampacity
8
5
5.5
3.5
Two current levels were investigated on each test setup:
• 15 Amps
• 600% Maximum Full Load Ampacity
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Issued: 8-10-01
The first level was selected to link the overload testing with a common branch circuit current level
recognized in the industry. The second level was selected to link up with UL508 testing for the overload
relays and to simulate a locked rotor condition on a motor. The overload relay was sized according to
the maximum permissible load current during the overload testing. Opening time was recorded for each
test. Visual inspection and dielectric testing of the wire was conducted.
Non-Motor Loads
Testing in this area consisted of a single branch circuit overcurrent protective device sized per the
ampacity of the conductor. As a result of the work conducted by the NFPA79 committee, limitations
were placed on the load current for 16 and 18 AWG conductors, See Annex A for details on this
analysis. These current levels are shown in Table 16. Note that these values are 80% of the ampacities
shown in Table 1.
Table 16
Maximum Full Load Currents (for Non-Motor Loads)
16 AWG
18 AWG
Maximum Full Load Ampacity
Maximum Full Load Ampacity
8
5.6
Two current levels were investigated on each test setup:
• 135% Overcurrent Protective Device Rating
• 600% of Maximum Full Load Ampacity
The first level was selected based upon a common overload test level conducted on branch circuit
overcurrent protective devices. The second was selected to simulate a higher level overload condition
that might exist.
Inspection of Wire
In order to verify if a conductor passes the overload and short-circuit testing, a two step investigation
was used. The first step is a common practice in testing today. Immediately following the tests, a visual
inspection was performed on the conductor and observations were noted.
Acceptability of Results
Visual damage to the insulated wire including insulation damage, wire pulled out of terminal, or
vaporization of the wire would result in a failure for the test. If a failure of the visual test resulted, the
dielectric test was not conducted.
Insulation Dielectric Withstand Tests
The second step in the wire acceptance testing was a dielectric withstand test. It was determined that the
dielectric withstand test in UL83, Thermoplastic Insulated Wire and Cable, section 27 would be used.
Perform Dielectric Voltage-Withstand Test as specified in UL83 section 27.
• Immerse as much of the insulation of the wire as possible in room temperature tap water for a period
of not less than 6 hours.
• With wire still immersed in the tap water, attach one lead of a dielectric voltage tester to the bare
ends of the wire. Attach the other lead to a conducting material that is immersed in the water.
• Apply 2000V to the wire under test for 60 seconds.
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Issued: 8-10-01
Acceptability of Results
The wire shall be able to withstand the applied voltage without breakdown for the said amount of time.
See Annex C for a flow chart representation of the testing sequence used in this investigation.
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TEST DATA, OBSERVATIONS, AND RESULTS
Data, observations, and results obtained from the testing in this study are outlined in this section. Results
from each test are outlined in three main sections:
Test Data Sheet
This section provides information relating to the setup of the test, a description of the test, test circuit
parameters, and test results.
Test Observations
This section provides a frame by frame view from the NTSC VHS video that was taken during the testing.
The frames shown are the six frames surrounding the test.
Assessment of Results
This section links the results of the testing to the analysis that was conducted on withstand ratings of
conductors prior to the testing. The data accumulated during the testing was compared to the withstands
shown in Table 16.
Table 16
ICEA I t Withstand Limits Copper Conductor, Thermoplastic Insulation
Wire Size
Short-circuit Withstand I2 t
18 AWG
7,355 A2 s
16 AWG
18,657 A2 s
2
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E4273
Issued: 8-10-01
TEST #:
1A
Purpose: Verification of Overload Protection - Class 10
Overload Relay
Description: 16 AWG type MTW wire
Class 10 overload relay set at 8 Amps
Protective device is a 20 Amp Class CC fuse
16 AWG
Class 10
Relay
Test Parameters
Current:
15 A
TEST DATA:
Relay opened in 5 seconds
Fuse did not open
Results:
Visual:
No Visible Damage
Dielectric: Passed
19
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Issued: 8-10-01
Assessment of Results
Test 1A:
Overload relay opened in 5 seconds.
Fuse did not open. There was no visible damage to the conductor. The conductor passed the
dielectric test.
20
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Issued: 8-10-01
TEST #:
1B
Purpose: Verification of Overload Protection - Class 10
Overload Relay
Description: 16 AWG type MTW wire
Class 10 overload relay set at 8 Amps
Protective device is a 20 Amp Class CC fuse
16 AWG
Class 10
Relay
Test Parameters
Current:
48 A (600%)
TEST DATA:
Relay opened in 2 seconds
Fuse did not open
Results:
Visual:
No Visible Damage
Dielectric: Passed
21
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Issued: 8-10-01
Assessment of Results
Test 1B:
Overload relay opened in 2 seconds.
Fuse did not open. There was no visible damage to the conductor. The conductor passed the
dielectric test.
22
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Issued: 8-10-01
TEST #:
1C
Purpose: Verification of Overload Protection - Class 20
Overload Relay
Description: 16 AWG type MTW wire
Class 20 overload relay set at 8 Amps
Protective device is a 20 Amp Class CC fuse
16 AWG
Class 20
Relay
Test Parameters
Current:
15 A
TEST DATA:
Relay opened in 4.9 seconds
Fuse did not open
Results:
Visual:
No Visible Damage
Dielectric: Passed
23
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Issued: 8-10-01
Assessment of Results
Test 1C:
Overload relay opened in 4.9 seconds.
Fuse did not open. There was no visible damage to the conductor. The conductor passed the
dielectric test.
24
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TEST #:
Issued: 8-10-01
1D
Purpose: Verification of Overload Protection - Class 20
Overload Relay
Description: 16 AWG type MTW wire
Class 20 overload relay set at 8 Amps
Protective device is a 20 Amp Class CC fuse
16 AWG
Class 20
Relay
Test Parameters
Current:
33 A (600%)
TEST DATA:
Relay opened in 3.13 seconds
Fuse did not open
Results:
Visual:
No Visible Damage
Dielectric: Passed
25
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Issued: 8-10-01
Test 1D:
Overload relay opened in 3.13 seconds.
Fuse did not open. There was no visible damage to the conductor. The conductor passed the
dielectric test.
26
E4273
TEST #:
Issued: 8-10-01
1E
Purpose: Verification of Overload Protection - Fuse Only
Description: 16 AWG type MTW wire
Protective device is a 10 Amp Class CC fuse
16 AWG
Test Parameters
TEST DATA:
Fuse cleared in 5 min. 48 sec.
Current: 13.51 A (135%)
Results:
Visual:
No Visible Damage
Dielectric: Passed
27
E4273
Issued: 8-10-01
Test 1E:
Fuse opened in 5 minutes 48 seconds. There was no visible damage to the conductor. The
conductor passed the dielectric test.
28
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Issued: 8-10-01
TEST #:
1F
Purpose: Verification of Overload Protection - Fuse Only
Description: 16 AWG type MTW wire
Protective device is a 10 Amp Class CC fuse
16 AWG
Test Parameters
TEST DATA:
Fuse cleared in 4.6 seconds
Current:
48 A (600%)
Results:
Visual:
No Visible Damage
Dielectric: Passed
29
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Issued: 8-10-01
Test 1F:
Fuse opened in 4.6 seconds. There was no visible damage to the conductor. The conductor passed
the dielectric test.
30
E4273
Issued: 8-10-01
TEST #:
2A
Purpose: Verification of Overload Protection - Class 10
Overload Relay
Description: 18 AWG type MTW wire
Class 10 overload relay set at 6 Amps
Protective device is a 15 Amp Class CC fuse
18 AWG
Class 10
Relay
Test Parameters
Current:
15 A
TEST DATA:
Relay opened in 6 seconds
Fuse did not open
Results:
Visual:
No Visible Damage
Dielectric: Passed
31
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Issued: 8-10-01
Test 2A:
Overload relay opened in 6 seconds.
Fuse did not open. There was no visible damage to the conductor. The conductor passed the
dielectric test.
32
E4273
Issued: 8-10-01
TEST #:
2B
Purpose: Verification of Overload Protection - Class 10
Overload Relay
Description: 18 AWG type MTW wire
Class 10 overload relay set at 6 Amps
Protective device is a 15 Amp Class CC fuse
18 AWG
Class 10
Relay
Test Parameters
Current:
30 A (600%)
TEST DATA:
Relay opened in 3 seconds
Fuse did not open
Results:
Visual:
No Visible Damage
Dielectric: Passed
33
E4273
Issued: 8-10-01
Test 2B:
Overload relay opened in 3 seconds.
Fuse did not open. There was no visible damage to the conductor. The conductor passed the
dielectric test.
34
E4273
Issued: 8-10-01
TEST #:
2C
Purpose: Verification of Overload Protection - Class 20
Overload Relay
Description: 18 AWG type MTW wire
Class 20 overload relay set at 6 Amps
Protective device is a 15 Amp Class CC fuse
18 AWG
Class 20
Relay
Test Parameters
Current:
15 A
TEST DATA:
Relay opened in 5.8 seconds
Fuse did not open
Results:
Visual:
No Visible Damage
Dielectric: Passed
35
E4273
Issued: 8-10-01
Test 2C:
Overload relay opened in 5.8 seconds.
Fuse did not open. There was no visible damage to the conductor. The conductor passed the
dielectric test.
36
E4273
TEST #:
Issued: 8-10-01
2D
Purpose: Verification of Overload Protection - Class 20
Overload Relay
Description: 18 AWG type MTW wire
Class 20 overload relay set at 6 Amps
Protective device is a 15 Amp Class CC fuse
18 AWG
Class 20
Relay
Test Parameters
Current: 20.96 A (600%)
TEST DATA:
Relay opened in 3.8 seconds
Fuse did not open
Results:
Visual:
No Visible Damage
Dielectric: Passed
37
E4273
Issued: 8-10-01
Test 2D:
Overload relay opened in 3.8 seconds.
Fuse did not open. There was no visible damage to the conductor. The conductor passed the
dielectric test.
38
E4273
Issued: 8-10-01
TEST #:
2E
Purpose: Verification of Overload Protection - Fuse Only
Description: 18 AWG type MTW wire
Protective device is a 7 Amp Class CC fuse
18 AWG
Test Parameters
TEST DATA:
Fuse cleared in 35 seconds
Current:
9.51 A (135%)
Results:
Visual:
No Visible Damage
Dielectric: Passed
39
E4273
Issued: 8-10-01
Test 2E:
Fuse opened in 6 minutes 35 seconds. There was no visible damage to the conductor. The
conductor passed the dielectric test.
40
E4273
Issued: 8-10-01
TEST #:
2F
Purpose: Verification of Overload Protection - Fuse Only
Description: 18 AWG type MTW wire
Protective device is a 7 Amp Class CC fuse
18 AWG
Test Parameters
TEST DATA:
Fuse cleared in 5.4 seconds
Current:
34 A (600%)
Results:
Visual:
No Visible Damage
Dielectric: Passed
41
E4273
Issued: 8-10-01
Test 2F:
Fuse opened in 5.4 seconds. There was no visible damage to the conductor. The conductor passed
the dielectric test.
42
E4273
Issued: 8-10-01
TEST #:
3A
Purpose: Verification of Short-Circuit Protection - Low
Level
Description: 1 foot of 16 AWG type MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 20 amp Class CC umbrella fuse.
1 AWG, 4’
16 AWG, 1’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
3
Phase Clearing I2t x 10
A
1.03
B
1.53
C
0.81
482 Vac
5.2 KA
72 %
Ip x 103
0.98
1.69
0.91
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
43
Comments
Fuse Opened
Fuse Opened
Fuse Opened
E4273
Issued: 8-10-01
Test #: 3A
Test 3A:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
1,530 A2 s
1,690 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. There
was no visual damage to any of the conductors. Video footage showed little activity, with minor
movement of the conductors. All the conductors passed the dielectric test.
44
E4273
Issued: 8-10-01
TEST #:
3B
Purpose: Verification of Short-Circuit Protection - Medium
Level
Description: 1 foot of 16 AWG type MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 20 amp Class CC umbrella fuse.
1 AWG, 4’
16 AWG, 1’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
3
Phase Clearing I2t x 10
A
0.578
B
1.98
C
0.561
484 Vac
10.9 KA
76 %
Ip x 10 3
1.15
2.31
1.35
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
45
Comments
Fuse Opened
Fuse Opened
Fuse Opened
E4273
Issued: 8-10-01
Test #: 3B
Test 3B:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
1,980 A2 s
2,310 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. There
was no visual damage to any of the conductors. Video footage showed little activity, with minor
movement of the conductors. All the conductors passed the dielectric test.
46
E4273
Issued: 8-10-01
TEST #:
3C
Purpose: Verification of Short-Circuit Protection - High
Level
Description: 1 foot of 16 AWG MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 20 amp Class CC umbrella fuse.
1 AWG, 4’
16 AWG, 1’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
Phase Clearing I2t x 103
A
0.77
B
1.42
C
0.24
482 Vac
53.6 KA
13.5 %
Ip x 103
2.28
3.15
1.14
Results:
Visual: No Visual Damage on any Phase
Dielectric: Passed
47
Comments
Fuse Opened
Fuse Opened
Fuse Did Not Open
E4273
Issued: 8-10-01
Test #: 3C
Assessment of Results
Test 3C:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
1,420 A2 s
3,150 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. There
was no visual damage to any of the conductors. Video footage showed little activity, with minor
movement of the conductors. All the conductors passed the dielectric test.
48
E4273
Issued: 8-10-01
TEST #:
4A
Purpose: Verification of Short-Circuit Protection - Low
Level
Description: 1 foot of 18 AWG type MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 20 amp Class CC umbrella fuse.
1 AWG, 4’
18 AWG, 1’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
Phase
A
B
C
482 Vac
5.2 KA
72 %
Clearing I2t x 10
0.77
1.42
0.6
3
Ip x 10
0.83
1.65
0.83
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
49
3
Comments
Fuse Opened
Fuse Opened
Fuse Did Not Open
E4273
Issued: 8-10-01
Test #: 4A
Test 4A:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
1,420 A2 s
1,650 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. There
was no visual damage to any of the conductors. Video footage showed little activity, with minor
movement of the conductors. All the conductors passed the dielectric test.
50
E4273
Issued: 8-10-01
TEST #:
4B
Purpose: Verification of Short-Circuit Protection - Medium
Level
Description: 1 foot of 18 AWG type MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 20 amp Class CC umbrella fuse.
1 AWG, 4’
18 AWG, 1’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
3
Phase Clearing I2t x 10
A
0.384
B
1.44
C
0.536
484 Vac
10.9 KA
76 %
Ip x 10 3
0.797
2.07
1.42
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
51
Comments
Fuse Did Not Open
Fuse Opened
Fuse Opened
E4273
Issued: 8-10-01
Test #: 4B
Test 4B:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
1,440 A2 s
2,070 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. There
was no visual damage to any of the conductors. Video footage showed little activity, with minor
movement of the conductors. All the conductors passed the dielectric test.
52
E4273
Issued: 8-10-01
TEST #:
4C
Purpose: Verification of Short-Circuit Protection - High
Level
Description: 1 foot of 18 AWG type MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 20 amp Class CC umbrella fuse.
1 AWG, 4’
18 AWG, 1’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
Phase
A
B
C
482 Vac
53.6 KA
13.5 %
Clearing I2t x 103
0.77
1.45
0.14
Ip x 10 3
2.54
3.3
0.84
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
53
Comments
Fuse Opened
Fuse Opened
Fuse Did Not Open
E4273
Issued: 8-10-01
Test #: 4C
Test 4C:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
1,450 A2 s
3,300 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. There
was no visual damage to any of the conductors. Video footage showed little activity, with minor
movement of the conductors. All the conductors passed the dielectric test.
54
E4273
Issued: 8-10-01
TEST #:
5B
Purpose: Verification of Short-Circuit Protection - Medium
Level
Description: 4 feet of 18 AWG type MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 30 amp Class CC, J, and T
umbrella fuse.
1 AWG, 4’
18 AWG, 4’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
3
Phase Clearing I2t x 10
A
5.17
B
7.01
C
4.52
484 Vac
10.9 KA
76 %
Ip x 10 3
2.15
3.54
2.15
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
55
Comments
Fuse Opened
Fuse Opened
Fuse Opened
E4273
Issued: 8-10-01
Test #: 5B
Test 5B:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
7,010 A2 s
3,540 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. Video
footage showed little activity, with minor movement of the conductors. All conductors passed the
dielectric test.
56
E4273
Issued: 8-10-01
TEST #:
5C
Purpose: Verification of Short-Circuit Protection - High
Level
Description: 4 feet of 18 AWG type MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 30 amp Class CC, J, and T
umbrella fuse
1 AWG, 4’
18 AWG, 4’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
3
Phase Clearing I2t x 10
A
4.75
B
5.14
C
1.17
484 Vac
53.6 KA
13.5 %
Ip x 10 3
4.41
4.65
0.86
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
57
Comments
Fuse Opened
Fuse Opened
Fuse Did Not Open
E4273
Issued: 8-10-01
Test #: 5C
Test 5C:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
5,140 A2 s
4,650 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. Video
footage showed little activity, with minor movement of the conductors. All conductors passed the
dielectric test.
58
E4273
Issued: 8-10-01
TEST #:
6B
Purpose: Verification of Short-Circuit Protection - Medium
Level
Description: 100 feet of 16 AWG type MTW wire per phase
3 phase bolted fault on load side of motor starter.
Protective device is a 20 amp Class CC umbrella fuse.
1 AWG, 4’
16 AWG, 1’
Motor
Starter
16 AWG, 100’
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
Phase
A
B
C
484 Vac
10.9 KA
76 %
3
Clearing I2t x 10
0.82
0.57
0.75
Ip x 10
0.64
0.49
0.96
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
59
3
Comments
Fuse Opened
Fuse Opened
Fuse Did Not Open
E4273
Issued: 8-10-01
Test #: 6B
Test 6B:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
820 A2 s
960 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. Video
footage showed little activity, with minor movement of the conductors. All conductors passed the
dielectric test.
60
E4273
Issued: 8-10-01
TEST #:
6C
Purpose: Verification of Short-Circuit Protection - High
Level
Description: 100 feet of 16 AWG type MTW wire per phase
3 phase bolted fault on load side of motor starter.
Protective device is a 20 amp Class CC umbrella fuse.
1 AWG, 4’
16 AWG, 1’
Motor
Starter
16 AWG, 100’
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
3
Phase Clearing I2t x 10
A
1.23
B
0.65
C
0.62
484 Vac
53.6 KA
13.5 %
Ip x 10 3
0.7
0.92
0.43
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
61
Comments
Fuse Opened
Fuse Opened
Fuse Did Not Open
E4273
Issued: 8-10-01
Test #: 6C
Test 6C:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
1,230 A2 s
920 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. Video
footage showed little activity, with minor movement of the conductors. All conductors passed the
dielectric test.
62
E4273
Issued: 8-10-01
TEST #:
6E
Purpose: Verification of Short-Circuit Protection - Medium
Level
Description: 100 feet of 18 AWG type MTW wire per phase
3 phase bolted fault on load side of motor starter.
Protective device is a 20 amp Class CC umbrella fuse.
1 AWG, 4’
18 AWG, 1’
Motor
Starter
18 AWG, 100’
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
Phase
A
B
C
484 Vac
10.9 KA
76 %
Clearing I2t x 10 3
1
0.7
0.51
Ip x 10 3
0.55
0.6
0.45
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
63
Comments
Fuse Opened
Fuse Opened
Fuse Did Not Open
E4273
Issued: 8-10-01
Test #: 6E
Test 6E:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
1,000 A2 s
600 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. Video
footage showed little activity, with minor movement of the conductors. All conductors passed the
dielectric test.
64
E4273
Issued: 8-10-01
TEST #:
6F
Purpose: Verification of Short-Circuit Protection - High
Level
Description: 100 feet of 18 AWG type MTW wire per phase
3 phase bolted fault on load side of motor starter.
Protective device is a 20 amp Class CC umbrella fuse.
1 AWG, 4’
18 AWG, 1’
Motor
Starter
18 AWG, 100’
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
3
Phase Clearing I2t x 10
A
0.86
B
1.28
C
0.92
484 Vac
53.6 KA
13.5 %
Ip x 10 3
0.61
0.59
0.52
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
65
Comments
Fuse Opened
Fuse Opened
Fuse Did Not Open
E4273
Issued: 8-10-01
Test #: 6F
Test 6F:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
1,280 A2 s
610 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. Video
footage showed little activity, with minor movement of the conductors. All conductors passed the
dielectric test.
66
E4273
Issued: 8-10-01
TEST #:
7A
Purpose: Verification of Short-Circuit Protection – Low
Level
Description: 1 foot of 18 AWG type MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 30 amp Class CC, J, and T
umbrella fuse.
1 AWG, 4’
18 AWG, 1’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
Phase
A
B
C
630 Vac
5 KA
76 %
Clearing I2t x 103
6.73
8.29
4.67
Ip x 10 3
1.76
1.45
2.97
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
67
Comments
Fuse Opened
Fuse Opened
Fuse Did Not Open
E4273
Issued: 8-10-01
Test #: 7A
Test 7A:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
8,290 A2 s
2,970 Amps
Maximum clearing I2 t let through during this test was above the calculated withstand level. There
was no visible damage to any of the conductors. Video footage showed little activity, with minor
movement of the conductors. All the conductors passed the dielectric test.
68
E4273
Issued: 8-10-01
TEST #:
7B
Purpose: Verification of Short-Circuit Protection - Medium
Level
Description: 1 foot of 18 AWG type MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 30 amp Class CC, J, and T
umbrella fuse.
1 AWG, 4’
18 AWG, 1’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
Phase
A
B
C
604 Vac
10.7 KA
71 %
3
Clearing I2t x 10
2.88
10.4
3.35
Ip x 10
1.55
3.86
2.42
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
69
3
Comments
Fuse Did Not Open
Fuse Opened
Fuse Opened
E4273
Issued: 8-10-01
Test #: 7B
Test 7B:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
10,400 A2 s
3,860 Amps
Maximum clearing I2 t let through during this test was above the calculated withstand level. There
was no visible damage to any of the conductors. Video footage showed little activity, with minor
movement of the conductors. All the conductors passed the dielectric test.
70
E4273
Issued: 8-10-01
TEST #:
7C
Purpose: Verification of Short-Circuit Protection - High
Level
Description: 1 foot of 18 AWG type MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 30 amp Class CC, J, and T
umbrella fuse.
1 AWG, 4’
18 AWG, 1’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
3
Phase Clearing I2t x 10
A
6.22
B
0.19
C
6.33
608 Vac
52.7 KA
8.5 %
Ip x 10 3
5.23
0.66
5.18
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
71
Comments
Fuse Opened
Fuse Opened
Fuse Did Not Open
E4273
Issued: 8-10-01
Test #: 7C
Test 7C:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
6,330 A2 s
5,230 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. There
was no visible damage to any of the conductors. Video footage showed little activity, with minor
movement of the conductors. All the conductors passed the dielectric test.
72
E4273
Issued: 8-10-01
TEST #:
8A
Purpose: Verification of Short-Circuit Protection – Low
Level
Description: 1 foot of 18 AWG type MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 30 amp Class CC, J, and T
umbrella fuse.
1 AWG, 4’
18 AWG, 1’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
Phase
A
B
C
482 Vac
5.2 KA
72 %
3
Clearing I2t x 10
6.06
7.07
4.76
Ip x 10
1.81
2.91
1.83
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
73
3
Comments
Fuse Opened
Fuse Opened
Fuse Opened
E4273
Issued: 8-10-01
Test #: 8A
Test 8A:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
7,070 A2 s
2,910 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. There
was no visible damage to any of the conductors. Video footage showed little activity, with minor
movement of the conductors. All the conductors passed the dielectric test.
74
E4273
Issued: 8-10-01
TEST #:
8B
Purpose: Verification of Short-Circuit Protection - Medium
Level
Description: 1 foot of 18 AWG type MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 30 amp Class CC, J, and T
umbrella fuse.
1 AWG, 4’
18 AWG, 1’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
3
Phase Clearing I2t x 10
A
1.68
B
8.12
C
2.95
484 Vac
10.9 KA
76 %
Ip x 10 3
1.54
3.74
2.32
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
75
Comments
Fuse Did Not Open
Fuse Opened
Fuse Opened
E4273
Issued: 8-10-01
Test #: 8B
Test 8B:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
8,120 A2 s
3,740 Amps
Maximum clearing I2 t let through during this test was above the calculated withstand level.
There was no visible damage to any of the conductors. Video footage showed little activity, with
minor movement of the conductors. All the conductors passed the dielectric test.
76
E4273
Issued: 8-10-01
TEST #:
8C
Purpose: Verification of Short-Circuit Protection - High
Level
Description: 1 foot of 18 AWG type MTW wire per phase
3 phase bolted fault on line side of motor starter.
Protective device is a 30 amp Class CC, J, and T
umbrella fuse.
1 AWG, 4’
18 AWG, 1’
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
Phase
A
B
C
482 Vac
53.6 KA
13.5 %
Clearing I2t x 103
4.21
7.9
2.3
Ip x 10 3
3.75
5.63
2.52
Results:
Visual:
No Visual Damage on any Phase
Dielectric: Passed
77
Comments
Fuse Opened
Fuse Opened
Fuse Did Not Open
E4273
Issued: 8-10-01
Test #: 8C
Test 8C:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
7,900 A2 s
5,630 Amps
Maximum clearing I2 t let through during this test was above the calculated withstand level. There
was no visible damage to any of the conductors. Video footage showed little activity, with minor
movement of the conductors. All the conductors passed the dielectric test.
78
E4273
Issued: 8-10-01
TEST #:
9B
Purpose: Verification of Short-Circuit Protection - Medium
Level for Various Grounding Schemes
Description: 10 inches of 18 AWG type MTW
1 phase bolted fault on line side of motor starter.
Protective device is a 30 amp Class CC, J, and T
umbrella fuse.
1 AWG, 4’
18 AWG, 10”
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
3
Phase Clearing I2t x 10
A
B
C
6.69
484 Vac
10.9 KA
76 %
Results:
Visual:
No Visual Damage
Dielectric: Passed
79
Ip x 10 3
2.83
Comments
Fuse Opened
E4273
Issued: 8-10-01
Test #: 9B
Test 9B:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
6,690 A2 s
2,830 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. Video
footage showed little activity, with minor movement of the conductor. The conductor passed the
dielectric test.
80
E4273
Issued: 8-10-01
TEST #:
9C
Purpose: Verification of Short-Circuit Protection - High
Level for Various Grounding Schemes
Description: 10 inches of 18 AWG type MTW
1 phase bolted fault on line side of motor starter.
Protective device is a 30 amp Class CC, J, and T
umbrella fuse.
1 AWG, 4’
18 AWG, 10”
Motor
Starter
Short Created
Here
Test Parameters
TEST DATA:
Voltage:
Current:
pf:
3
Phase Clearing I2t x 10
A
6.13
B
C
484 Vac
53.6 KA
13.5 %
Results:
Visual:
No Visual Damage
Dielectric: Passed
81
Ip x 10 3
3.81
Comments
Fuse Opened
E4273
Issued: 8-10-01
Test #: 9C
Test 9C:
Maximum Clearing I2 t
Maximum Peak Current Ip
=
=
6,130 A2 s
3,810 Amps
Maximum clearing I2 t let through during this test was below the calculated withstand level. Video
footage showed little activity, with minor movement of the conductor. The conductor passed the
dielectric test.
82
E4273
Issued: 8-10-01
REPORT BY:
REVIEWED BY:
GEORGE R. GOLDING
Senior Project Engineer
Conformity Assessment Services
DAVID A. DINI
Senior Research Engineer
Research Department
83
E4273
Issued: 8-10-01
Bibliography
Canadian Standards Association Std C22.1-98. Canadian Electrical Code, 1998 editon.
CSA, Ontatario, Canada.
Fink, Donald G., and H. Wayne Beaty. Standard Handbook for Electrical Engineers, 13th edition.
Mcgraw-Hill, Inc., 1993
Gregory, George D. “Single-Pole Short-Circuit Interruption of Molded-Case Circuit Breakers.”
IEEE Industrial & Commercial Power Systems Technical Conference. IEEE, New York, 1999
Insulated Cable Engineers Association, Inc. “Short Circuit Characteristics of Insulated Cable”
Insulated Cable Engineers Association Publication P-32-382. , 1969
International Association of Electrical and Electronic Engineers Std. ANSI/IEEE 141-1993.
Electric Power Distribution for Industrial Plants, IEEE Red Book. IEEE, New York, 1993
International Association of Electrical and Electronic Engineers Std. ANSI/IEEE 241-1990.
Electric Power Distribution for Commercial Buildings, IEEE Gray Book. IEEE, New York, 1990.
International Association of Electrical and Electronic Engineers Std. ANSI/IEEE 242-1986.
Protection and Coordination of Industrial and Commercial Power Systems, IEEE Buff Book.
IEEE, New York, 1986.
International Association of Electrical and Electronic Engineers Std. ANSI/IEEE 1015-1997.
Applying Low-Voltage Circuit Breakers Used in Industrial and Commercial Power Systems,
IEEE Blue Book. IEEE, New York, 1997
International Association of Electrical Inspectors. Soares Book on Grounding, 7th Edition.
IAEI, Richardson, TX, 1999
International Electrotechnical Commission Std. 60364-4-43. “Protection Against Overcurrent.” , 1997
Middendorf, W.H. “Life Characteristics Of Insulated Wire Subjected To Short Time, High Current
Faults.” IEEE Transactions on Electrical Insulation. Vol. EI-15 No.5, October 1980
Middendorf, W.H. “Life Characteristics of Medium Size Insulated Wire Subjected To Short Time, High
Current Faults.” IEEE Transactions on Electrical Insulation. Vol. EI-20 No.3, June 1985
Middendorf, W.H. “Effects Of Short-Time, High-Current Faults On Aged, Insulated Wire.”
IEEE Transactions on Electrical Insulation. Vol. EI-21 No.2, April 1986
National Fire Protection Association Std. ANSI/NFPA70. National Electrical Code, 1999 edition.
NFPA, Quincy, MA
84
E4273
Issued: 8-10-01
National Fire Protection Association Std. ANSI/NFPA79. Electrical Standard for Industrial Machinery,
1997 edition. NFPA, Quincy, MA.
Underwriter Laboratories Standard for Safety ANSI/ANCE/UL/CSA248. Low-Voltage Fuses.
UL, Northbrook,IL, 2000.
Underwriter Laboratories Standard for Safety ANSI/UL489. Molded-Case Circuit Breakers, Molded-Case
Switches, and Circuit Breaker Enclosures. UL, Northbrook,IL, 2000.
Underwriter Laboratories Standard for Safety ANSI/UL508. Industrial Control Equipment.
UL, Northbrook,IL, 2000.
85
E4273
Issued: 8-10-01
ANNEX A
The following outlines the work and recommendations conducted by the NFPA79 committee.
The new exceptions in NFPA79, prior to the ROP meetings, would read:
13.6 Conductor sizing.
Conductors shall not be smaller than:
13.6.1 Power circuits
No. 14
Exception 1: No. 16 shall be permitted where applied as follows:
a) For non-motor power circuits of 8 amperes or less where protected in accordance with
Clause 7 and with Class CC fuses rated at not more than 10 amperes,or
b) For motor loads with a full load ampacity of 8 amperes or less, where protected with
Class CC fuses at not more than 250% of full load ampacity, and Class 10 overload
protection per UL 508, or
c) For motor loads with a full load ampacity of 5.5 amperes or less, where protected with
Class CC fuses at not more than 250% of full load ampacity, and Class 20 overload
protection per UL 508, and
d) Where part of a jacketed multiconductor cable assembly or flexible cord, or as individual
conductors when used in a cabinet or enclosure.
Exception 2: No. 18 shall be permitted where applied as follows:
a) For non-motor power circuits of 5.6 amperes or less where protected in accordance with
Clause 7 and with Class CC fuses rated at not more than 7 amperes, or
b) For motor loads with a full load ampacity of 5 amperes or less, where protected with
class CC fuses at not more than 250% of full load ampacity, and Class 10 overload
protection per UL 508, or
c) For motor loads with a full load ampacity of 3.5 amperes or less, where protected with
class CC fuses at not more than 250% of full load ampacity, and Class 20 overload
protection per UL 508, and
d) Where part of a jacketed multiconductor cable assembly or flexible cord, or as individual
conductors in a cabinet or enclosure.
Substantiation: The present parts of NFPA 79-1997 15.3 were re-identified to match the
numbering sequence.
These proposed new exceptions permit the use of 16/18 AWG conductors, and factory assembled
16/18 AWG multi-conductor cables, in small motor branch circuit applications. This exception
86
E4273
Issued: 8-10-01
will also allow a common, desirable, practice unutilized on small horsepower, multi-motor
machinery.
Wire sizes of 0.75 mm2 and 1 mm2 are commonly applied where the load currents are very small
in applications based upon the IEC 60204-1. Wire sizes of 0.75 mm2 and 1 mm2 have an
ampacity similar to 18 AWG and 16 AWG wire respectively.
Conservative based calculations were evaluated relative to short circuit and overload concerns.
After considering many variables, it was determined that a similar use of 18 AWG and 16 AWG
wire would constitute a reasonable approach and give application guidance to a present practices
under the detailed requirements as proposed in 13.6.1 Exceptions 1 and 2.
In order to limit exposure to physical damage the use of these conductors would be limited to
multiconductor cables, and to individual conductors when used in a cabinet or enclosure.
The following information is provided to detail the evaluation process.
16 AWG Data
Time
Area (CM)
Isc (Amps)1
.004
2580
2160
.008
2580
1527
.0167
2580
1057
0.1
2580
432
1
2580
137
5
2580
61
10
2580
43
20
2580
31
30
2580
25
1
Data based upon ICEA (Insulated Cable Engineers Association) insulation Damage Formulas
UL508 Test Points
Class
Current @ 600% 2
10
40
20
33
2
Value shown in table is based upon 6 X the limited current specified in the proposed 13.6.1
UL 248 Test Point @ 50KA
Time (sec)
Max Current Allowed (Amps)
.004
707 3
3
2
Current Level Extrapolated from UL I t limit by dividing out time (.004)
87
E4273
Issued: 8-10-01
18 AWG Data
Time
Area (CM)
Isc (Amps)4
.004
1620
1356
.008
1620
959
.0167
1620
664
0.1
1620
271
1
1620
86
5
1620
38
10
1620
27
20
1620
19
30
1620
16
4
Data based upon ICEA (Insulated Cable Engineers Association) insulation Damage Formulas
UL508 Test Points
Class
Current @ 600% 5
10
30
20
21
5
Value shown in table is based upon 6 X the limited current specified in the proposed 13.6.1
UL 248 Test Point @ 50KA
Time (sec)
Max Current Allowed (Amps)
.004
707 6
6
2
Current Level Extrapolated from UL I t limit by dividing out time (.004)
The Insulated Cable Engineers Association (ICEA) tables for insulation damage was used to
create the worst case condition for the wire. The formula as developed by ICEA is based upon
an adiabatic process where all the heat will be contained within the wire(conductor). This does
not take into account the heat bleed off into the terminations and components. As a result, a
damage curve was generated for thermoplastic insulation at 150 deg. C. This was the worst case
of the three main types evaluated by ICEA which include:
-
thermoplastic (150 deg. C)
rubber, paper, varnished cloth (200 deg. C)
crosslinked polyethylene & ethylene propylene rubber (250 deg. C)
This damage curve then supplied the worst possible condition to which the wire (conductor)
would be subjected.
After laying the groundwork for wire damage, various overcurrent protective devices were
reviewed.
Current limiting devices were decided upon in order to cover the variety of fault current
conditions that could apply to a machine. Upon examination of Underwriters Laboratories (UL)
“General Information for Electrical Equipment” (White Book), let-through I2 T of various current
88
E4273
Issued: 8-10-01
limiting branch circuit fuses were considered. Selecting Class CC fuses and protecting 16 and 18
AWG wire according to UL limits allowed a maximum let-through current to be determined.
Next, motor controller characteristics were explored. Based upon the information provided in
UL508, test points were plotted on the time current curve to evaluate the performance of the
overload device under long term heating conditions. (Note: Under these conditions there is a
high probability the heat will be dissipated from the conductor into the terminals and associated
components).
Guidelines were selected for proper fuse sizing and maximum full load current rating of motors
based upon the above data. The criteria for determining the maximum full load current rating
was (1) the maximum current value the conductor could handle for the set amount of time (10
sec for class 10, etc.), (2) add 10% for a conservative heat bleed off factor, and (3) divide by 6
per the requirements of UL 508. This then derived the FLC value.
16 AWG
100
Time (sec)
10
Insulation Damage 16
AWG
Class 10
1
Class CC Fuse
Class 20
0.1
0.01
0.001
1
10
100
1000
Current (amps)
89
10000
E4273
Issued: 8-10-01
18 AWG
100
10
1
Time (sec)
Insulation Damage 18 AWG
Class 10
Class 20
Class CC
0.1
0.01
0.001
1
10
100
1000
10000
Current (amps)
Following the NFPA79 ROP meetings the wording of this section was revised to read:
13.6 Conductor sizing.
Conductors shall not be smaller than:
13.6.1 Power circuits
No. 14
Exception 1: No. 16 shall be permitted where applied as follows:
a) For non-motor power circuits of 8 amperes or less where protected in accordance with
Clause 7 and with branch circuit rated circuit breakers listed for use with No.16 wire or
Class CC,J, or T fuses rated at not more than 10 amperes, or
b) For motor loads with a full load ampacity of 8 amperes or less, where protected in
accordance with Clause 7 and with branch circuit rated circuit breakers listed for use
with No.16 wire or Class CC,J, or T fuses, and Class 10 overload protection per UL 508,
or
c) For motor loads with a full load ampacity of 5.5 amperes or less where protected in
accordance with Clause 7 and with branch circuit rated circuit breakers listed for use
90
E4273
Issued: 8-10-01
with No.16 wire or Class CC,J, or T fuses, and Class 20 overload protection per UL 508,
and
d) Where part of a jacketed multiconductor cable assembly or flexible cord, or as individual
conductors when used in a cabinet or enclosure.
Exception 2: No. 18 shall be permitted where applied as follows:
a) For non-motor power circuits of 5.6 amperes or where protected in accordance with
Clause 7 and with branch circuit rated circuit breakers listed for use with No.18 wire or
Class CC,J, or T fuses rated at not more than 7 amperes, or
b) For motor loads with a full load ampacity of 5 amperes or less, where protected in
accordance with Clause 7 and with branch circuit rated circuit breakers listed for use
with No.18 wire or Class CC,J, or T fuses, and Class 10 overload protection per UL 508,
or
c) For motor loads with a full load ampacity of 3.5 amperes or less, where protected in
accordance with Clause 7 and with branch circuit rated circuit breakers listed for use
with No.18 wire or Class CC,J, or T fuses, and Class 20 overload protection per UL 508,
and
d) Where part of a jacketed multiconductor cable assembly or flexible cord, or as individual
conductors in a cabinet or enclosure
91
E4273
Issued: 8-10-01
ANNEX B
The following table shows the data for the umbrella fuses used in this testing:
Umbrella Fuse Data
Fuse Type
20A Umbrella #1
20A Umbrella #2
20A Umbrella #3
30A Umbrella #1
30A Umbrella #2
30A Umbrella #3
Test
Current
Amps x 103
52
52
52
52
52
52
Power
Factor
.15
.15
.15
.15
.15
.15
UL/CSA/ANCE 248
I2 t Umbrella Limit
(A 2 sec x 103 )
2
2
2
7
7
7
92
Clearing I2 t
A 2 sec x 103
3.47
4.17
4.36
13.6
14.4
14.4
UL/CSA/ANCE 248
Ip Umbrella Limit
(Amps x 103 )
3
3
3
6
6
6
Peak Let
Through (Ip)
Amps x 103
3.99
4.13
4.27
6.53
6.59
6.58
E4273
Issued: 8-10-01
ANNEX C
93
E4273
Issued: 8-10-01
94
E4273
Issued: 8-10-01
95
E4273
Issued: 8-10-01
96
E4273
Issued: 8-10-01
Index
adiabatic, 5, 8
American National Standards
ANSI, 6
bolted fault, 14
Bolted fault conditions, 13
class 10 overload relay, 15
class 20 overload relay, 15
conductor
dielectric strength of, 5
Insulation Dielectric Withstand Tests, 16
magnetic withstand, 9
magnetic withstands, 13
maximum short-circuit temperatures, 5
short-circuit protection of, 6
short-circuit thermal withstand, 9
visual inspection, 16
withstand capabilities, 4
Electrical Code
Canadian, 7
National, 3, 4, 8
fuse
I2t, 9, 13
instantaneous peak current, 9, 13
grounding
Corner grounded Delta, 14
Resistance grounded WYE, 14
Solidly grounded WYE, 14
Ungrounded systems, 14
various schemes, 12, 14
ICEA, 4, 5, 7, 8, 18
Standard P-32-382, 4
IEC, 7
IEC60364-4-43 1997, 7
IEC 60204-1, 3
Safety of Machinery - Electrical Equipment, 3
IEEE
ANSI/IEEE 141-1993
Red Book, 6
ANSI/IEEE 241-1990
Gray Book, 6
ANSI/IEEE 242-1986
Buff Book, 6
Institute of Electrical and Electronics Engineers, 6
Insulated Cable Engineers Association
Standard P-32-382, 4
insulation
damage, 5
Machinery Standards
IEC60204-1 1997, 7
NFPA79, 3
SAE HS-1738 2000, 7
Middendorf, 4, 5, 6
NFPA79, 1, 3, 4, 8, 9, 10, 13, 16, 86
NFPA79 adhoc committee, 15
Onderdonk, 4, 6
Soares, 4, 6
UL White book, 9
UL248, 9, 10, 12, 13
UL489, 12, 13
"bus bar" high fault circuit test configurations, 13
“Bus bar” test high fault circuit test configurations,
12
UL508, 4, 10, 12, 13
UL83, 12
Insulation Dielectric Testing, 16
umbrella fuses, 12, 13
umbrella limits, 9
validity rating, 6
Withstand Ratings, 4
97